Electronic watermarking is well known in the art. Generally, in electronic watermarking a watermark signal of some kind is added to an electronic representation of an item, such as a recording or a broadcast signal. The added watermark signal known in the art may provide an indication of origin intended to provide traceability of a copied representation; and/or may indicate specific rights of a holder of the electronic representation, such as a right to use or play but no right to copy, or right to copy at reduced quality. Generally, implementation of such specific rights is termed “controlling access”, and the field of controlling access is also referred to as “conditional access”; these terms are used with the indicated meanings throughout the present specification and claims. Typically, in the case of specific rights associated with a watermark, conditional access is enforced by all legitimate devices which are operative to access, play back, or otherwise utilize the electronic representation.
Added watermark signals may be added to a certain place in an electronic representation or may be “spread out” so that the watermark signal is found in many parts of the electronic representation. Added watermark signals may be easily perceived by one who plays back the representation, or may not be discernible upon normal playing of the representation.
The art of adding a signal, including a watermark signal, to a medium in order to embed information which is not easily discernible upon normal examination or playback is generally termed “steganography”.
U.S. Pat. No. 5,606,609 to Houser et al describes an electronic document verification system and method in which a security object is embedded in an electronic document such as, for example, with an object linking and embedding (OLE) capability. Typically, the security object includes security information and an identifier for invoking the processing of the security information.
U.S. Pat. No. 5,607,188 to Bahns et al describes a technique of marking an optical disc for customized identification, in which a watermark is applied to a master disc, preferably by modifying the periodic diffraction grating effect created by encoded data in the disc.
U.S. Pat. No. 5,636,292 to Rhoads describes steganography methods employing embedded calibration data on a carrier to be identified, the methods being intended to provide robustness despite degradation of the carrier and permeation of an imbedded signal throughout the carrier.
U.S. Pat. No. 5,659,726 to Sandford, II et al describes a method of embedding auxiliary information into a set of host data, in which pixels in the host data which are nearly identical and which have values differing by less than an intrinsic noise value are manipulated and replaced with auxiliary data.
U.S. Pat. No. 5,664,018 to Leighton describes a watermarking process in which each of a set of copies of a work has a slightly modified form of a baseline watermark placed within a critical region of the data, the slight variations not being perceptually visible and not interfering with the work.
U.S. Pat. No. 5,687,236 to Moskowitz et al describes a steganographic method and device for encoding and decoding information into a stream of digitized samples, in which the information is contained in the samples, not prepended or appended to the sample stream. The method of Moskowitz et al is used to establish ownership of copyrighted digital multimedia content and to provide a disincentive to piracy.
Published PCT application WO 96/41468 describes a method and apparatus for copyright protection of various recording media using a combination of a video finger print signal and an authenticating signature. The authenticating signature is designed in such a way that it will not be transferred to illicit copies made on CD receivers. When a copy of a protected CD is played the absence of the authenticating signature causes the player to prohibit the disk from playing normally.
Published PCT application WO 97/13248 describes an electronic watermarking scheme which operates at a high level in the hierarchy of the (MPEG) source signal, thus attempting to ensure that the watermark is easily detectable but difficult to erase.
Published PCT application WO 97/22206 describes a method for marking a video and/or audio signal to identify, for example, that the signal is authentic and is not to be copied.
Published PCT application WO 97/26732 describes a method for stega-protection of computer code, encoding the code into a data resource with a digital watermark, the digital watermark containing licensing information interwoven with essential code resources.
Published PCT application WO 97/26733 describes a method for an encrypted digital watermark in which pseudo-random keys for encoding and decoding digital watermarks are generated and applied with human assistance.
Published PCT application WO 97/34391 describes a watermarking process intended to be resistant to collusion attacks.
Published PCT application WO 98/02864 describes optimization methods for insertion, protection and detection of digital watermarks based on individual characteristics of a given digital stream.
Published PCT application WO 98/03014 describes a method for detecting a water mar-k embedded in an information signal by con-elating the information signal with a plurality of watermarks.
European Patent Application 0 651 554 A1 describes a method and apparatus for addition and removal of digital watermarks in a hierarchical image storage and retrieval system, a digital watermark being added in a selected image resolution component and the means to remove it in an additional image component.
Israel Patent Application 120174, assigned to the same assignee as the present application, describes a digital protection system in which encryption control messages (ECMs) in a first format are replaced with ECMs in a second format. Corresponding applications, all assigned to the same assignee as the present application, include: U.S. patent application Ser. No. 09/014,791; published UK Patent Application 9725557.4, and published EPO Patent Application 98300596.8.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.